1. Field of the Invention
This invention relates to a pantograph slipper or sliding strip for current collectors which have an elongated carrier and an elongated carbon brush supported by the carrier, as well as a method for the manufacture of the slipper.
2. Description of the Prior Art
Conventional pantograph slippers for current collectors, as used, for example, on electrically powered rail vehicles, are conventionally produced by securing a carbon brush to the upper side of a carrier which is usually made of metal. The brush is appropriately secured to the carrier, for example by bonding, soldering and/or mechanically wedging the two to each other. The carrier supports the carbon brush and is used for securing the slipper to a current collector.
The manufacture of such conventional slippers has several disadvantages. One disadvantage is that electric arcing can occur between the overhead wire touched by the slipper and exposed surfaces of the metal carrier. Moisture and especially ice that may form on the collector enhance the likelihood that arcing may take place. Such arcing can damage the slipper and particularly the metal carrier thereof. Another disadvantage results from differential thermal expansions of the carbon brush and the carrier. Operating temperature changes can differentially expand the two elements, which can lead to a deformation of the entire slipper similar to the manner in which bimetals bend as a result of temperature changes. This can cause mechanical damage, especially to the carbon brush, and can lead to a thermal overstressing of the bond between the brush and the carrier. Finally, the manufacture of conventional pantograph slippers is relatively costly, to a significant extent because a secure, permanent and highly stressable connection between the carbon brush and the separately manufactured carrier must be established.
Pantograph slippers which have interiorly arranged carriers are disclosed in German patents 431,365 and 671,946 as well as Austrian patents 139,525 and 140,894. These references disclose a tubular carbon brush made of serially arranged, multiple sections and a metal carrier which is disposed inside and surrounded by the brush. The carrier is tubular and it is secured to the brush in one of two ways. The carrier is either longitudinally slit and prestressed, so that it engages the inner surface of the brush (Austrian patent 139,525), or the space between the carrier and the brush is filled with a cast material (Austrian patent 140,894) if the brush or its segments are nonrotatably supported on the carrier (German patents 431,365 and 506,064). Since the carbon of the carbon brush can be subjected to only limited tension, the use of prestressed carriers on the hollow interior of the brush is relatively unsatisfactory. Further, the casting material between the carrier and the carbon brush does not form an optimal mechanical and electrical connection between the two.